After a consideration of the ways in which the fertility of domestic animals is controlled some of the factors which limit it have been investigated. Various circumstances control the number of ova shed at each heat period. Data are presented which show that the low fertility of young as compared with adult sows is due to the fact that not so many ova are shed at each period.

Counts have been made of the number of corpora lutea present in the ovaries and number of foetuses present in the uteri of pregnant rabbits and pigs. The results show that many more ova are shed at the heat period than young are produced at birth. Some ova possibly may be lost but many after fertilization atrophy at some period of their development and undergo absorption in utero.

While the occurrence of atrophic foetuses only causes reduced fertility in animals which have many young at birth yet their occurrence in animals producing only one young would give rise to sterility so that the problem of the cause of the atrophy becomes an important one.

Investigation points to the conclusion that the atrophy is not bacterial in origin since frequently healthy and atrophic foetuses lie side by side in the uterus. Moreover no bacteria could be found either in the foetus or foetal membranes.

Evidence is given to show that nutrition cannot be the cause of the atrophy although it may affect to a certain extent the size of the young.

No conclusion has yet been arrived at as to the cause of the atrophy, and the several possibilities suggested are still under investigation.

The relationship between the exchangeable potassium content of a soil and the activity ratio, aK/√(aCa+Mg), of the solution with which it is in ‘instantaneous equilibrium’ is a characteristic of the soil which is independent of the soil: solution ratio or the total electrolyte concentration (up to O·06 M) of the solution. It is unaffected by the transfer of substantial amounts of potassium ions to or from the fixed state. Hence instantaneous equilibrium curves provide a basis against which to measure the changes in exchangeable potassium content due to fixation and release. This procedure has the important advantages that all measurements are made in the solution phase and that the solutions in contact with the soil approximate to the natural soil solution.

The technique has been employed successfully in studying the fixation and release of potassium by several widely different soils.

The results confirm that fixation or release are determined by the extent to which the soil contains more or less exchangeable potassium than its equilibrium percentage potassium saturation. Seemingly the equilibrium percentage potassium saturation, and hence the equilibrium activity ratio of potassium in the soil solution aK/√(aCa+Mg), is regulated by the amounts or proportions of potassium in the fixed state. The amounts or proportions of potassium in the fixed state may be increased by repeated applications of potassium fertilizers and reduced by continued cropping.

Increasingly serious shortages of water make it imperative to improve the efficiency of irrigation in agriculture, horticulture and in the maintenance of urban landscapes. The main aim of the current review is to identify ways of meeting this objective. After reviewing current irrigation practices, discussion is centred on the sensitivity of crops to water deficit, the finding that growth of many crops is unaffected by considerable lowering of soil water content and, on this basis, the creation of improved means of irrigation scheduling. Subsequently, attention is focused on irrigation problems associated with spatial variability in soil water and the often slow infiltration of water into soil, especially the subsoil. As monitoring of soil water is important for estimating irrigation requirements, the attributes of the two main types of soil water sensors and their most appropriate uses are described. Attention is also drawn to the contribution of wireless technology to the transmission of sensor outputs. Rapid progress is being made in transmitting sensor data, obtained from different depths down the soil profile across irrigated areas, to a PC that processes the data and on this basis automatically commands irrigation equipment to deliver amounts of water, according to need, across the field. To help interpret sensor outputs, and for many other reasons, principles of water processes in the soil–plant system are incorporated into simulation models that are calibrated and tested in field experiments. Finally, it is emphasized that the relative importance of the factors discussed in this review to any particular situation varies enormously.

Since the 1970s, the delivered sugar yield per hectare has risen at an average annual rate of 0·111 t/ha, while the sugar yield in the official variety trials has increased at an average annual rate of 0·204 t/ha. These increases are usually considered to be the result of improvements in varieties and in beet agronomy. The present paper considers the possible impact of recent changes in climate on UK sugar yields by using the Broom's Barn Crop Growth Model and daily weather data collected over the last 30 years. Simulations of sugar yield using weather in eastern England since 1976 increased by an average annual rate of 0·139 t/ha, which accounted for about two thirds of the rate in the official variety trials. This increase was not an artefact of the accuracy of weather recording but it was, in part, accounted for by the trend to earlier sowing. Although it was not statistically significant, the earlier sowing trend was associated with an increase of 0·025 t/ha per year and was an indirect effect of the climate change. The annual deviations from these trends have not tended to become significantly bigger or smaller over the three decades. The model is not variety-specific, so it makes no allowance for variety improvements during the last 30 years. Clearly, varieties have improved so the implication must be that some of the changes in agronomy have tended to decrease the yields significantly. The changes in agronomic practice most likely to be responsible are the extension of the crop processing campaign, leading to greater post-harvest storage losses, and a decrease in the irrigated area.

Soya beans, like other legumes, contain low concentrations of the nutritionally essential sulphur amino acid, methionine. Cysteine, although not an essential amino acid because it can be synthesized from methionine, also influences the nutritional quality of soya bean products when it is only present in low levels. A low cysteine content will also aggravate a methionine deficiency. Soya bean lines deficient in 7S protein subunits have been identified. The 7S proteins contain substantially less methionine and cysteine than the 11S proteins. With the myriad of genetic null alleles for these subunits it may be possible to tailor the 7S/11S storage protein ratio and their total composition in seeds to include only those subunits with the richest sulphur amino acid composition. Cotyledon feeding experiments, using isolated soya bean cotyledons, demonstrated that addition of methionine to the culture media caused increased synthesis of both proteins and free amino acids but the mechanism by which this takes place is not clear. Biotechnological approaches to improve nutritional value of soya beans include elevated expression of genes that originate from other species which encode high-sulphur proteins. High level expression of a 2S Brazil nut albumin gene in soya bean resulted in raised methionine concentration although the Brazil nut gene is highly antigenic and therefore will not be useful in production agriculture. Modification of glycinin to increase sulphur amino acid content is possible, and these gene products are capable of normal assembly into trimers in vitro although are rapidly degraded in vivo by the asparaginyl endopeptidase responsible for post-translational modification of proglycinin. Solutions to the methionine deficiency may be anticipated from a combination of approaches followed in laboratories worldwide. Many of these approaches are not without difficulty but, despite this, the likelihood is that soya beans with improved nutritional quality (which may not be confined to sulphur-containing amino acids as other nutritionally essential amino acids are also valuable) will be available in the near future. It will be essential to confirm that the increased total methionine (or other amino acid) is digestible to the animal to at least the same degree as conventional cultivars.

The artificial fibre bag technique has been widely used in studies of forage dry-matter digestibility (Van Keuren & Heinemann, 1962) and of the release of a range of plant constituents during fermentation in the rumen (Playne, McLeod & Dekker, 1972). More recently, the technique has been promoted as a simple means of estimating the rate and extent of food protein degradability in the rumen (θrskov & Mehrez, 1977; Mathers, Horton & Miller, 1977).

Development of the fibrous root system of sugar beet was studied by washing soil samples taken from field experiments through the growing season. At the beginning of June the root system was still poorly developed but during June there was rapid proliferation. In the top 70 cm there was only little further increase in root density after the end of June. Below 70 cm root density increased up to the end of August. Throughout the season fibrous root density decreased with depth. Despite the origin of the lateral roots from two grooves on the storage root, fibrous root distributions at each depth around individual plants were essentially uniform from mid-June onwards. In the absence of nitrogen fertilizer, fibrous root development exceeded that of a crop given fertilizer, particularly at depths greater than 50 cm early in the season. The maximum value of root density was 2·8 cm/cm3 soil recorded in the top 10 cm in mid-September. Compared with published data for other crops, the sugar-beet root system was sparser than that of winter wheat or maize but denser than that of a soya bean or cassava.

Soil water content was measured with a neutron probe. Inflows to roots were calculated from soil water content changes in different soil layers. In the top 30 cm, inflows ranged up to 10·8 μl water/cm root.day and were up to five times higher than published inflows for winter wheat. At 30–100 cm sugar beet and winter wheat inflows were generally similar. The 0–30 and 30–120 cm layers contributed about 80 and 20% respectively of the total water use by sugar beet while no uptake was recorded below 110 cm. Previous studies have shown that sugar beet often takes up water from soil deeper than 110 cm, although it is not unknown for the depth of water removal to be restricted.

1. Calorimetric experiments on the utilization of dietary energy by the laying White Leghorn hen are described.

1. A study was made of the effects of feeding regimen and the composition of the diet on the ruminal production of V.f.a.'S in cattle.

2. The day-to-day variations in the pattern of rumen fermentation in cows given a diet of hay and concentrates indicated that within-cow differences in the molar proportions of the acids from diet to diet are of significance if they exceed about 3% (of the mean value) for acetic acid, about 10% for propionic and butyric acids, and about 25% for valeric acid. The results emphasized also the important differences to be found between cows given the same diet.

3. A change in the frequency of feeding from once to four times daily at a constant daily drymatter intake had little effect on the daily mean values for pH, concentration of total V.f.a.'S, or the molar percentages of the individual acids, but almost invariably decreased the range of values observed between feeding.

4. With diets of hay and of hay and concentrates an increase in daily dry-matter intake was associated with a fall in pH and an increase in the concentration of total V.f.a.'S; with the diet of hay and concentrates there was a considerable decrease in the molar percentage of acetic acid and a corresponding increase in N-butyric, but there was little change in the molar percentages of the acids with the diet of hay.

Intake and faecal and urinary output of nitrogen, potassium and phosphorus by steers grazing high quality pasture at either of two intake levels were measured in three trials lasting 10–12 days. Intake was estimated from total faecal D.M. and in vitro D.M. digestibility of hand-plucked pasture. A known proportion of urine was sampled by a nonsurgical technique.

Average urinary mineral output between trials ranged from 93 to 134 g N/day, or 40 to 51% of consumed N; 74 to 137 g K/day or 33 to 76 % of consumed K and no more than 1 g P/day, or 2 to 4% of consumed P. Faeces contained 36–62 g N/day, or 16–24% of consumed N; 12–46 g K/day, or 8–21% of consumed K and 10–23 g P/day, or 44–74% of consumed P. The volume of urine passed differed widely between days for individual steers and between steers within each trial. In trial 3, daily output ranged between 5–8 and 54.71 by different animals. For two steers over three 24 h periods, frequency of urination ranged between 13 and 73/24 h; urine volumes between 7.6 and 51.2 1/24 h; urinary excretion of N between 81 and 137 g/24 h and of K between 58 and 90g/24h.

Urinary N and K concentrations were higher at night than during the day, ranging in trial 3 from 0.8 to 14.1 mg N/l, and 0.6 to 9.9 mg K/l. No clear diurnal patterns were found for P.

Results are reported from nine field trials carried out in 1985/86 and 1986/87 aimed at identifying plant traits which are associated with high yield in barley in low-rainfall Mediterranean areas. Thirtyseven two-rowed and 35 six-rowed genotypes, representing the known diversity in traits considered to be useful, were compared in trials at three sites differing in expected annual rainfall (212–328 mm) in northern Syria, and in droughted and irrigated trials at Cambridge, UK. Yield, its components and other morphological and developmental traits were measured and correlations calculated.

Grain yields of the two- and six-rowed groups of genotypes were similar at all sites except in the irrigated trial in Cambridge, where the six-rowed genotypes gave the highest yield. Aside from the known difference in number of ears and number of grains/ear between two- and six-rowed genotypes, the simple correlations between grain yield and measured traits suggested that important traits for high yield in two- and six-rowed genotypes in dry environments were prostrate habit, vigorous seedling growth, good ground cover, early ear emergence, many ears/m2 and large grains. In the two-rowed genotypes, short stature and a short grain-filling period were also important, while in the six-rowed genotypes, tall stature, high straw yield, many grains/ear and long peduncles were important. Correlations of these characters with an index of drought susceptibility and with yield adjusted for yield potential and date of ear emergence supported the conclusions based on the simple correlations.

The physiological basis of the correlated traits is discussed and the implications for breeding are considered.

Four low and four high methane (CH4) emitters were selected from a flock of 20 Romney sheep on the basis of CH4 production rates per unit of intake, measured at grazing using the sulphur hexafluoride (SF6) tracer technique. Methane emissions from these sheep were monitored at grazing for four periods (P): October, November, January and February 1999/2000. All measurements were carried out on perennial ryegrass/white clover pasture under generous herbage allowance, and the sheep were maintained on similar pastures during non-measurement periods. The tracer technique was used for all the CH4 measurements and feed DM intake was calculated from total faecal collection and estimated DM digestibility. Data for liveweight (LW), gross energy intake (GEI) and CH4 emission were analysed using split-plot analysis of variance. In addition, a between-period rank order correlation analysis was carried out for CH4 emission data.

Low CH4 emitters were heavier (P<0·05) than the high emitters in all the periods, but they did not differ (P<0·05) in their gross energy intakes (GEI: MJ/kg LW0·75). Low and high CH4 emitters consistently maintained their initial rankings in CH4 yield (% GEI) throughout the subsequent periods and the correlation analysis of rank order for CH4 yield showed strong between-period correlation coefficients, although this was weaker in the last period. It is suggested that feeding conditions that maximize feed intake (e.g. generous allowance of good quality pasture under grazing) favour the expression and persistence of between-sheep differences in CH4 yield.

The efficiency of digestion and absorption is dependent upon the rate at which digesta moves through the gastrointestinal tract. The following report describes the gastrointestinal transit for digesta markers given to ten species of mammals fed the same diet.

1. Four groups of half-brother-sister lambs of eight individuals, each of balanced sexes, have been reared on quantitatively different planes of nutrition so as to grow along predetermined growth curves until they reached 30 lb. dressed carcass weight when killed. Treatment differences started at the end of the third month of foetal life. One group was reared on a High Plane of nutrition throughout (High – High), another on a High Plane up to 6 weeks of post-natal life followed by a Low Plane (High-Low), the third on a Low Plane up to 6 weeks after birth, followed by a High Plane (Low-High), and the fourth on a Low Plane throughout (Low-Low). The High-High lambs were killed at 9 weeks old, the High-Low and Low-High at 15 weeks and the Low-Low at 41 weeks old. This allowed for comparison of animals of the same carcass weight but different age and of animals of the same age and carcass weight, but having differently shaped growth curves. The relative effects of the treatments on the development of the body proportions and carcass quality have been studied.

2. The proportion of dressed carcass to organs and offals was highest (48·9% of live weight) in the High-High group, lowest (42·9%) in the Low-Low, and intermediate in the High-Low (45·6%) and Low-High (46·3%). Variation in carcass percentage due to sex was not significant, though 4·8% higher in the females than in the wethers of the High-High group.

3. The weight of the head is more affected by the age of the animal than by the plane of nutrition or the carcass weight, it being of the same weight in the Low-High and High-Low lambs, but significantly lighter in the High-High and significantly heavier in the Low-Low groups. The skin, with wool, was much heavier in the Low-Low than in the other groups, while the weight of the blood was directly affected by the plane of nutrition prior to slaughter, it being significantly heavier in the High-High and Low-High groups than in the High-Low and Low-Low ones.

4. The development of the brain and the eyes was found to be primarily a function of age, these organs being lightest in the High-High and heaviest in the Low-Low group. The brain (as in Part I) appeared to be earlier maturing than the eyes, the differences between the age groups all being significant in the case of the latter, but only the High-High lambs had significantly lighter brain than the other groups.

5. Marked differential effects due to the plane of nutrition and/or age on some of the internal organs were observed, though others like the heart appear to be a function of body weight, being equally well developed in all treatment groups.

6. Organs like the thymus glands, the liver, the spleen, the kidneys and the small intestines are for their development, like the blood, found to be more dependent on the level of nutrition at the time of slaughter than on age or carcass weight, being heavier in the High-High and the Low-High groups than in either the High-Low or the Low-Low. These differences are in most cases highly significant.

7. The development of organs like the oesophagus, the rumen, the reticulum, the omasum and the genital organs, appears to be more influenced by age than the plane of nutrition, while that of the abomasum, the caecum, the large intestines, the rectum and the pancreas is influenced by the plane of nutrition as well as age.

8. Apart from the urinogenital organs, the pancreas is the only organ which exhibits a significant difference due to sex, being 14% heavier in the males.

9. In general, the organs appear to have priority claim for the available nutrients in the blood stream to allow them to develop to such an extent, which enables them to cope with their function at any age. When the nutritive supply is low, organs, whose function is directly associated with growth, suffer proportionately more than those which are of primary importance for life, like the brain, the eyes and the heart.

10. The four treatments produced two distinct types of carcasses. The High-High and the Low-High carcasses were of very similar conformation, short in the leg, blocky and well covered with subcutaneous fat, with the late maturing trunk joints proportionately better developed compared with the HighLow and Low-Low carcasses, which in conformation resembled each other, and were leggy, lank and badly covered with subcutaneous fat. In the latter two groups the early developing legs and neck were proportionately better developed than the later maturing trunk joints.

11. Marked differential effects were produced on the carcass composition. Bone in the dressed carcass was significantly lighter in the Low-Low than in the other groups, due to the inhibiting effects of continuous undernutrition on growth in thickness of bone. The difference in bone weight between the other groups was insignificant, though the High-Low had the heaviest bone in the carcass. Muscle was better developed in the High-Low and the Low-Low groups than in the Low-High and High-High groups, while fat, especially the subcutaneous fat, was better developed in the two latter groups.

12. A High Plane of nutrition prior to slaughter appears to be essential for good development of the latest maturing tissue, the subcutaneous fat. Under limited food supply the earlier maturing tissues, muscle and bone, especially for growth in length, have priority claim for the available nutrients.

13. The ewes had significantly lighter bone, slightly lighter muscle, though insignificantly so, and significantly heavier fat than the wethers.

14. As between the tissues, so within the anatomical units of each, marked differential effects were produced. Limited nutritive supply at any age causes greatest inhibiting effects on the tissues or those parts of any one tissue, which have the highest growth intensity at that age. Similarly, good nutrition at any age benefits most the parts of highest growth intensity at that time.

15. All tissues show great recuperative capacity if provided with adequate food supply after restricted nutrition, unless at that time they have passed their age of high growth intensity.

16. A Low Plane of nutrition from 6 to 15 weeks following high feeding, in the High-Low lambs, had the effect that not only was the subcutaneous fat, the tissue of highest growth intensity at that age, more retarded in development than the other earlier maturing tissues, but all the tissues were relatively more affected in the later maturing regions of the body than in the earlier maturing parts. On the contrary, a High Plane of nutrition from 6 to 15 weeks following severe undernutrition, in the Low-High lambs, resulted in proportionately better development of the subcutaneous fat than the other tissues, and within each tissue a proportionately better development in the late maturing regions of the body, as compared with the earlier developing parts. This is because of the relatively greater effect of the poor nutrition earlier on, on the parts of highest growth intensity during that period, and greater beneficial effects of the good nutrition afterwards on the parts which then had relatively higher growth intensity. Thus the bones of the leg (early maturing) were heavier in the High-Low than in the Low-High, while the ribs (late maturing) were heavier in the Low-High group. Muscle in the Low-High was heavier in the loin but lighter in the limbs and neck than in the High-Low, and the difference in fat in favour of the Low-High was much greater in the trunk joints than in the limbs, while the High-Low had even more fat in the neck.

17. Comparison of the development of the different anatomical units of the major tissues in the High-High and Low-Low carcasses showed that within each tissue the latest maturing parts suffered proportionately more from the continuous undernutrition, with the exception of the ribs, which, though the latest maturing part of the skeleton, were of the same weight in the Low-Low as the High-High, though total bone in the carcass was heavier in the latter. This is accounted for by the so late onset of high growth intensity in the ribs that the High-High lambs were killed before the ribs could benefit from the good nutrition as much as earlier maturing parts of the skeleton, while in the Low-Low, the ribs, having high growth intensity for a long time after the growth rate of earlier developing parts of the skeleton had declined, could compete for nutrients with considerable success with still later maturing tissues, muscle and fat.

18. In the skeleton the shape of individual bones was much more affected by the different treatments than their weight. This accounted for the great treatment differences in carcass conformation. The earlier maturing growth in length is much less affected than the later maturing growth in thickness, and the earlier maturing bones like the cannons are less affected than the later maturing femur or the pelvis.

19. The percentage of marbling fat in the longissimus dorsi muscle appeared to be more dependent on age of the animal than on the plane of nutrition or the state of fatness of the animal, being lowest in the High-High and highest in the Low-Low carcasses.

20. The iodine number of the marbling fat was also found to be more affected by the age of the animal than by the state of fatness or the plane of nutrition, it being highest in the High-High and lowest in the Low-Low carcasses.

21. The water content of the muscle was highest 78%) in the High-High lambs, but lowest in the Low-Low ones (74·9%).

22. The four treatments caused great and highly significant differential effects on the various carcass measurements. As some of these measurements have been found by previous workers to be even more important indices of meat quality than is the actual composition of the carcass, it may be claimed that the different treatments have affected carcass quality even more than carcass composition.

23. The treatment differences were proportionately much smaller in the external measurements, which are primarily indices of skeletal development, than in the internal muscle measurements and by far greatest in the fat measurements.

24. External measurements which should be small for desirable conformation like the leg length, F, the tibia plus tarsus, T, and the length of the cannon, M, were significantly greater in the Low-Low and the High-Low than in the other groups, being smallest in the High-High.

25. The most important muscle measurements, such as the depth of the eye muscle, B, and the shape index, B/A × 100, were best developed in the High-High, followed in a downward order by Low-High, High-Low and Low-Low groups.

26. The fat measurements were much better developed in the High-High and the Low-High groups than in the Low-Low and the High-Low ones.

27. The females had significantly better developed fat measurement than the wethers, while no significant sex differences were observed in the other measurements.

28. Considering the several factors studied which affect carcass quality, the High-High lambs yielded carcasses of the best quality, especially the females, closely followed by the Low-High ones, while the Low-Low carcasses were of much inferior quality and the High-Low still poorer. Those of the latter two groups were more typical of an unimproved late maturing breed than being of the same breed as the High-High and Low-High carcasses.

The apparent digestibility of a diet can be calculated from the amounts of food eaten and excreta voided. This ‘total collection’ method is laborious because it requires a period lasting several days. It can be circumvented by the inclusion in the diet of a suitable reference substance (Kotb & Luckey, 1972). From the concentration of the reference substance (marker) in the diet and in the droppings, apparent dry-matter digestibility can be calculated.

Organic materials with a C: N ratio ranging from about 85: 1 to about 10: 1 were submitted to nitrification tests in an acid and in an alkaline soil during a period of 6 months. In the acid soil only pea pod meal, with a C: N ratio of 13·3: 1 showed an increase in inorganic N over control; in the alkaline soil the limit above which no nitrification will occur within a period of 6 months was at C: N = 26: 1; below this limit the rate of nitrification increased rapidly with decreasing C: N ratio. Unnitrified N was left behind in a quantity corresponding to 1·5–2·2 per cent, of the original material, the percentage being higher in the case of materials rich in N.

All the materials tended to increase the content of “a-humus” in the soil, though not to the same extent or in the same manner. More “a-humus” was produced in the alkaline than in the acid soil, except in the case of farmyard manure. Straw, sweet clover, lupin and farmyard manure apparently acted both through their lignin content and through the synthesising action of microorganisms, since they increased the amounts of both N and methoxyl in humus. Mycelium of Polyporus contains a fraction possessing the properties of “humic acid,” rich in N, but devoid of methoxyl, which persists in the soil.

Studies of single soil organisms, while useful in specialized cases, e.g. Rhizobia and mycohrrizae, do not yield information on the functioning of the soil ecosystem. This is because most important soil processes, e.g. carbon and nitrogen mineralization, depend upon interactions between entire suites of organisms, many of which still await identification and most of which remain unculturable.

For many purposes, treating the soil microbial community as a single, undifferentiated unit, the soil microbial biomass (defined as all soil organisms <5000 μm3 volume), has much to commend it. It is analogous to studying the forest rather than an individual tree and uniquely permits an understanding of the soil–plant–microbe system as a whole, rather than studying only a small part. The present paper reviews the development of methods to measure microbial dynamics over the last century, the evolution of biomass methodologies and how they have helped the study of crucial soil processes such as nutrient and carbon cycling. Possible future directions for this research are also discussed and an explanation set forth of why the manipulation of this huge population (easily comprising 10 tonnes per hectare of living microbial cells in UK arable soils) has, so far, proved elusive.

1. The feed intake of four dry and of twenty pregnant and lactating ewes has been measured. Hay and dried grass cubes alone or in combination were studied on indoor conditions by direct measurement of intake and digestibility while the intake on grazing was measured by the chromic oxide-faecal nitrogen method.

2. For dry sheep, hay (61% O.M. digestibility) limited intake to 780 g. D.O.M./day and with added grass cubes there was a steady increase so that intake with cubes alone (although their apparent O.M. digestibility was 56%) was 1140 g. B.O.M./day. Pregnant ewes showed similar intakes and only with ewes carrying twins and triplets was there a slight decline in intake with advancing pregnancy.

3. The digestibilities of the diets were similar for pregnant, and lactating ewes.

The objective of this work was to investigate the effects of changing proportions of readily fermentable carbohydrate and fibre in the diet on the rates of lipolysis and fatty acid hydrogenation by sheep rumen digesta. Three experiments were carried out using rumen-fistulated Romney wethers. In the first experiment rumen digesta from one sheep on a high-fibre diet was incubated in vitro with [1–14C]linoleic acid and 0, 0·1, 0·2 and 0·5% sucrose. It was found that sucrose increased the rate of hydrogenation of linoleic acid by up to 40%.

In the second experiment five rumen-fistulated Romney wethers were fed five diets according to a latin-square experimental design. These diets had decreasing proportions of fibre (42·8–19·5%) and increasing proportions of starch (12·2–35·7%). Lipolysis and hydrogenation rates decreased significantly with decreasing fibre content which was reflected in the amounts of stearic and octadecenoic acids in the rumen digesta.

In the third experiment sheep were fed the high-fibre diet used in the first experiment and the rumen digesta incubated in the presence of 0, 0·15, 0·45, 0·75 and 1·50% starch. Lipolysis rates increased but no effect of added starch on hydrogenation was observed.

It was concluded that the short-term addition of energy to the rumen digesta increases lipolysis and hydrogenation rates. However, long-term replacement of fibre by starch results in a reduction of these rates.

Barley plants normally produce some tillers which die at an early stage, without bearing an ear. To investigate the proposition that these non-ear-bearing tillers may be wasteful of plant resources, two experiments were made in which the effect of tiller growth on the growth and final size of the main shoot was assessed. In one experiment, tillers were removed at a very early stage when they were a few mm long, or later when they were just emerging from the subtending leaf sheath. In the other experiment the main shoot was removed from the embryo and the size of the coleoptile tiller which grew in its absence was measured.

Tiller removal affected the growth and final size of the main shoot. Leaves emerged more quickly on the main shoot of the detillered plants and were bigger and sometimes more in number. The main shoot of the detillered plants was heavier and it bore a greater weight of grain because the ear had more and heavier grains. In the experiments where the main shoot was removed the coleoptile tiller produced more leaves, which emerged more rapidly and it bore more grains than the coleoptile tiller of the intact plants.

It is concluded that tillers, during their initiation and early growth, compete with the main shoot for a limited supply of resources, thus reducing the size of the main shoot. As some of the resources of the plant are used to produce tillers which die at an early stage and make no contribution to the final grain yield, it appears that they should be regarded as wasteful and that their production may reduce the final grain yield. The physiology of the initiation, growth and early death of these non-ear-bearing tillers requires further investigation.